Fixed gun interaircraft fire control system



Jan. 6, 1948. E. B. HAMMOND, JR, ETAL 2,433,843

FIXED GUN INTER-AIRCRAFT FIRE CONTROL SYSTEM Filed Oct. 17, 1942 4Sheefis-Sheet 1 FROM $TAB|LIZED RADIO (2R OPTICAL SIGHT 6 I 7 O- 8 11150H1 1 fll o ET /z I 1 0 COMPUTING MECHANISM 24- 25 26 27 all GUN FIRINGCIRCUIT I RUDDER SERVO ELEVATOR senvo AILERON SERVO E. B. HAMMOND, JR;ET AL FIXED GUN INTER-AIRCRAFT FIRE CONTROL SYSTEM Jan. 6, 1948.

.Filed Oct. 17, 1942 4 Sheets-Sheet 2 FIG. 3

.FIG.5

SEARCH AMR cam"! AME CATHODE m can)": INVENTORS! 5.5. HAMMOND JR.

y?" ATTORNEY i VOLTAGE Jan. 6, 1948. E. B. HAMMOND, JR, ET AL FIXED GUNINTER-AIRCRAFT FIRE CONTROL SYSTEM 4 Sheets-Sheet 4 Filed Oct. 1'7, 1942GUN FIRING CCT- AZ. AME

PENIJ CONT @ILER. AILER AME SERVO COMPUTING MECHANISM FIG.6

INVENTORS: E. B. HAMMOND J E. firr i 7 ATTORNEY Patented Jan. 6, 1948UNITED STATES PATENT OFFICE nxnn GUN INTERAIRCRAFT FlRE CONTROL SYSTEMEdmund B. Hammond, Jr., Brooklyn and Gifford E. White, Hempstead, N. Y.,assignors to Sperry Gyroscope Company, Inc., Brooklyn, N. Y., acorporation of New York Application October ll, 1942, Serial No. 462,44028 Claimsf (01. 89-375) l' The present invention is concerned withinteraircraft fire control apparatus especially adapted for use onfighter or interceptor aircraft which craft axis.

Presently usedinter-aircraft fire control systems for such fixed gunaircraft are very .ele-

mentary, comprising merely an optical sight whose axis is normallyparallel with respect to the gun and craft axis. A rough correction forsuperelevation is obtained by slightly offsetting the'sight axis withrespect to the gun axis in elevation, the amount of ofiset beingmanually varied in steps according to therange.

Since no computation of lead angle is made, it is not suflicient thatthe target be visible to the pilot in his sight; it is also necessarythat the lead angle, if one were computed, be substantially negligible.It is apparent that this condition obtains only when the range, andconsequently the time of flight, are very small, or when the pilot is onthe targets tail, that is, the line of sight is parallel to thedirection in which the target is moving. To meet the first of theseconditions,

the pilot is required to fly his plane in dangerously close to thetarget. To meet the second alternative condition, a large period -oftime, amounting to several minutes, is generally consumed after thetarget has first been sighted.

This same system, described above, is adapted to night flying by thprovision of suitable radio locating and position finding apparatus,which replaces the optical sight and performs essen-- tially the samefunctions. It is adapted to locate a target and provide indications on acathode ray tube indicator screen of the targets aximuth, elevation andslant range with respect to the plane. The pilot may then'fiy the planeuntil zero azimuth and elevation are indicated. If, at this time, theindicated slant range is sufliciently small, or if the zero indicationsof azimuth and elevation may be maintained while flying his own plane atconstant attitude (the target is then flying at constant attitude andhis own craft is on its tail) he may fire and expect a hit. Thus, thepreviously known system is even more difiicult. to use at night.

By the present invention it is proposed to overcome these disadvantagesby providing a suitable computing system so that the proper lead anglefor accurate fire may be automatically obtained, thus overcoming thenecessity of the pilot meeting the conditions that the lead angle benegligible, and allowing him to fire quickly after sight- 2 ing thetarget, and at a, distance limited-only by the range of his guns.

Inter-aircraft computers for flexibly or rotatably mounted guns areavailable, which indicat the correct gun aiming angles with respect tothe craft at which the guns must be positioned to effectively fire atthe target. Such computers have heretofore been used only on aircraftwhose guns are orientable with respect to th ship in elevation andazimuth. Obviously. on fixed gun aircraft, it becomes impossible toorient the guns with respect to the craft in accordance with thecomputed gun elevation (E3) and gun azimuth (Ag) angles, since, the gunsare fixed on the craft parallel to the craft axis, so that these anglesar fixed at zero.

In the present invention it is proposed to compute these angles, andthen fly thecraft in such a manner as to reduce them to zero. When thesecomputed angles are zero, the craft and guns are properly oriented toeffect a hit. Since, in the case of fixed gun aircraft the actual gunelevation (E and gun azimuth (Ag) angles must always be zero, it isbetter to consider the corresponding computed angles as elevation error(Eerror) and azimuth error (Aerror) angles, and as representing theangular displacement between the actual orientation of the craft and thecomputed orientation necessary to effect a hit.

In one embodiment of the present invention a simplified computingmechanism is disclosed which is adapted to be used on fighter andinterceptor aircraft. The invention is also described in connection witha known completely orientable and stabilized radio sight and a radioposition and direction finding system which is adapted to automaticallyand instantaneously supply the required data input to the computingmechanism. The invention also comprises an automatic pilot system,whereby the plane may be automatically flown in such a manner as toreduce' the computed elevation and azimuth error angles to zero.

Accordingly, the principal object of the present invention is to providean automatic interaircraft fire control system adapted for use onaircraft carrying fixed guns.

Another object of the invention is to provide a completely automaticpilot servo system adapted to fiy an aircraft carrying fixed guns iaccordance with computed signals in such a manner that the craft (andthe guns) will be correctly oriented for effective gun fire.

Still another object of the invention is to pro- A still further objectof the present invention is the provision of an automatic firingcircuit, whereby the gun can be fired only when the problem is correctlysolved, that is, when the craft and the gun are correctly oriented toeffect a hit.

An object of the invention is to provide an automatic and stabilizedradio-operated interaircraft fire control system for use on aircraftcarrying fixed guns.

Other objects and advantages will become apparent from the specificationtaken in connection v with the accompanying drawings, wherein oneembodiment of the invention is illustrated.

In the drawings,

Fig. 1 is a schematic representation of one embodiment of the presentinvention.

Fig. 2 is a schematic diagram of a detail of Fi 1.

Fig. 3 is an illustration useful in explaining the theory of operationof the invention.

Figs. 4A and 4B, taken jointly, show a schematic representationillustrating an embodiment of the system of the invention.

Fig. 5 shows a representative view of the I screen of the cathode rayindicator tube of Fig.

4A during search.

Fig. 6 shows a representative view of the screen of the cathode rayindicator tube of Fig. 4A dur ing track. 7

Fig. 7 is a wiring-diagram of the integral control units shownschematically in Fig. 4A.

Fig. 8 is a wiring diagram of a demodulator and filter circuit.

Similar characters of reference are used in all of the above figures toindicate corresponding parts. Arrows are used to indicate the directionof flow of information.

Fig. 1 illustrates an embodiment of the invention utilizing a computingmechanism I, which may be of any suitable type for computing leadangles, such as those of the well known K" series of sights widely usedby the armed forces. Other types of computers may be adapted for use inconnection with the present invention, such as those disclosed in thefollowing patents: Patent No. 2.105,985. issued January 18. 1938, toPapello; Patent No. 1,638,962, issued August 16, 1927, to Schneider;Patent No. 1,849,611, issued March 15, 1932, to Bussei: Patent No.

1,481,248, issued January 15, 1924, to Sperry;

and Patent No. 1,308,134, issued July 1919, to Wilson et al. The variouscomputers referred to are adapted to com ute the lead angle at which thegun must be ofiset from the line of sight in order that projectilestherefrom may strike a moving target. Generally, when the sight of acomputing gun sight of the kind referred to is displaced in tracking atarget, the computer is actuated by the sight or the sight displacingmeans according to the changing azimuth and elevation angles of thetarget. Depending on the type apparatus employed, the rate of change ofthese angles is determined either at the sight or within the computer,and multiplied by time of flight to obtain prediction components of thelead angle in azimuth and elevation, and to these components are addedcorresponding ballistic deflections, computed within the computer toobtain total lateral and total vertical deflections. Computers of thekind referred to are usually provided with separate output shaftsdisplaced respectively by the computing mechanism according to totallateral and total vertical deflections. Depending on the particulararrange-: ment of the apparatus, these outputs may be used to modify theposition of the guns or of the sight, the object being to effectrelative displacement of the guns and line of sight, so that theguns"lead" the line of sight according to the computed lead angle. It isproposed in the present invention to use the outputs of a lead anglecomputer as an aid or as controls to fly a supporting aircraft havingfixed'guns to a position wherein the guns are positioned in elevationand azimuth according to the lead angle computed by a computer. Such anarrangement is shown diagrammatically in Fig. 1.

At this point, the computing mechanism indicated by the oblong I will beconsidered as having but three input shafts, of which shafts 6 and I aredisplaced respectively by a sight, not shown, during. target trackingaccording to the instantaneous elevation angle E0 and the instantaneousazimuth angle A0. Shaft 8 is displaced manually or otherwise accordingto slant range, Do, obtained from a range finder, not shown.

The computing mechanism which may be of a type disclosed in any of theabove-mentioned patents or in any of the more recently developedcomputing. gun sights, such as the K series of sights referred to aboveis adapted to produce on suitable output shafts ii and I2, respectively,angular displacements corresponding to the gun elevation angle (Eg) andgun azimuth angle (Ag) with respect to the craft at which the guns mustbe positioned in order to effect a hit.

As previously pointed out, in aircraft carrying fixed guns, the guns arenot susceptible of being positioned in accordance with these computedangles, but, in fact, are fixed so that the actual gun elevation and gunazimuth angles (Eg, Ag) must always remain zero. Therefore, it isbetter, in a fixed gun system, to consider these angles as elevationerror angle (Eerror) and azimuth error angle (Aerror), and asrepresenting the angular displacement between the present attitude ofthe craft (and the guns) and the correct attitude of the craft (and theguns) required to effect a hit on the target. Henceforth, in thisdiscussion the computed gun elevation angle (Eg) and computed gunazimuth angle (Ag) will be referred to as elevation error angle (Eon-or)and azimuth error angle (Aerror) bearing in mind that they are, inreality, identical, the change in terminology merely representing achange in viewpoint better adapted to a fixed gun fire control system.The computed azimuth error angle (Aerror) signal, which appears as aproportional angular displacement of output shaft I2, is transmitted tothe rudder servo l5, as by pinion l3 and input rack I4. Rudder servo l5may be of the type shown in Fig. 2, to be further described in detail,or may be of any other suitable type adapted to produce a velocity ofoutput rack l6 proportional to the displacement of input rack IS. Theresulting motion of output rack i6 is then transmitted by pinion l1 andpulley system iii to the rudder which thereby alters the azimuthalattitude of the craft, which in turn alters the present azimuth angle(Ao) input data to the computer in such a sense that a smaller azimutherror angle (Aei'i'ol') will be computed. This process will continueuntil the computed azimuth error angle (Aerror) is reduced to zero,which means that the craft (and the guns) is at the proper azimuthalattitude to effect a hit.

This process is more clearly illustrated in Fig. 3 in which the angularrelations in azimuth for three successive stages in the process areshown. Wili be assumed that the target as is flying at 'and the targetis at the position To.

a constant velocity in the direction of the arrow 22, and that at thetime that the above described system begins to operate, the target andcraft l'ormula, Aemr=Ag=Ao+AA, and transmits this quantity to theautomatic servo control system for the rudder.

The resulting movement of the rudder alters the azimuthal attitude ofthe plane in such a direction as to increase A and to decrease Aerror,as indicated in the second stage of the diagram, which illustrates theangular relations at an instant later when the craft is at the positionC The last stage, in which the craft is shown at position C" and thetarget at position To", indicates the angular relations at a still latertime when this continuous process has finally reduced Aerror to zero.The craft (and the gums) is now at the correct azimuthal attitude toeffect a hit. It will be noted that at this time AA is equal and oppo-(Eel-m) data is transmitted by shaft ll, pinion l3, and rack l4 to tlheelevation servo, which then controls the elevator of the craft throughthe rack l6, pinion l1 and pulley system ill, in

such a sense as to reduce the elevation error angle (Eerror) to zero.

In Fig.1 there is also shown an automatic gun firing circuit consistingof leads 23, 24, battery 25, firing key 28, and gun firing solenoid 21.It will be understood that there is included in the .computingmechanism, and automatically operated thereby, two additional switchesin series with the gun firing circuit, one for elevation and one forazimuth, each of which is closed only when the corresponding elevationand azimuth error angle is zero, with the result that the gun may onlybe fired when both error angles are zero, that.

is, when the problem is correctly solved and a hit will be eilected.Such an automatic gun firing circuit will result in a saving ofammunition, and will make the pilots task simpler, since he may. in thiscase, continually hold his firing key closed, and the gun will fireautomatically only when the craft is correctly positioned to effect ahit.

There is also shown in Fig. 1 a servo control system which operates onthe aileron to provide the correct angle of bank for the craft while theattitude of the plane is being changed in azimuth. An inductive pick-oil40, which is adapted to sense the error in the angle of bank both inmagnitude and direction, transmits this information, in the form of analternating voltage across leads 38, 39, to the aileron amplifier 4|,which may be of any well known type adapted to produce across its outputleads 42, 43 a direct voltage corresponding in polarity and magnitude tothe phase and amplitude of the input signal voltage 38, 39. The aileronservo I" then operates on the ailerons under the control of signalvoltage 42, 43 through 6 y rack l3". pinion l1", and pulley system I."to provide the correct angle of bank.

The inductive pickil 40 consists essentially of a fixed core 30 of somemagnetic material, such as iron, and a suitably damped pendulous element35. The coil 3| wound on the center leg or core 33 is excited from aconstant source of altemating current 32. The coils 33 and on theopposing outer legs or core 33 are wound'oppositely on their respectivelegs and are connected in series, so that the voltage across leads 33and 33 will always be the difi'erence or the voltages induced in thecoils 33, 34.

The pendulous element 35 is mounted symmetrically with respect to thethree legs of the core 33, and is adapted to rotate about an axis 33which is parallel to'the longitudinal axis oi-the craft. Mounted on thependulous element 35, and

also symmetrically disposed with respect to the,

threelegs or core 30, there is shown an arcuate member 31 of a suitablemagneticmaterial, such as iron.

When the craft is operating at the proper angle of bank, the resultantof the gravitational force and the centrifugal force, which results fromany turn in azimuth, is in a direction parallel to the normally verticalaxis of the craft. When this condition obtains, the pendulous element35, which will assume the same direction as the resultant force, and themagnetic member 31, will .be symmetrically disposed with respect .to thethree legs of the core 30, which is fixed with respect to the craft. Thereluctance of the two parallel paths of the magnetic circuit being thenequal, equal fluxes will exist in both paths, with the result that thevoltages induced in coils 33 angle of bank. The inductive pick-ofi 40could be replaced by any suitable device capable of sensing themagnitude and direction of the necessary correction to the angle of bankand producing an output voltage proportional thereto.

Fig. 2 is an illustration of a suitable type 01 aileron servo whichcould be employed, although the present invention is not necessarilyrestricted to this type. As has previously been pointed out, theamplifier 4| is adapted to produce in its output leads 42, 43 areversible polarity direct voltage. This voltage 42, 43 controls asuitable torque motor 48 of any conventional type adapted to produce anangular displacement of its output member 43 in a direction and of amagnitude corresponding to the polarity and magnitude of the controlvoltage 42, 43.

As shown, output member 49 may be centralized by suitable springs 5|,which also assure a linear and proportionate type of control. Outputmember 49 is adapted to reciprocate the control piston 52 of a suitablecontrol valve 53, which is supplied with hydraulic or pneumatic pressurefrom a suitable pump, as by a duct 54, and is connected to a. returnreservoir or sump by a duct 56.

Valve 53 is adapted to produce between its output ducts 51 and 58 adiflerential fluid pressure corresponding in sense and magnitude to therelative displacement between its piston 52 and housing 55. Thisdifferential pressure is led to a servo motor 00, having a movablepiston 59 and a fixed housing The differential pressure causes piston 50to move, thereby causing rack I6" to be displaced at a velocityproportional to the displacement of control piston 52, and thereforealso proportional to the control voltage across leads 42. 43.

This same type of servo system may be used for the rudder servo I andfor the elevator servo I5. In this case, piston 52 of controlvalve 53would be actuated directlyby rack I3 or I3, as the case may be.

It will be understood, however, that the invention is not limited to thetype of servo system derepresent single conductors.

angle'(Amoi-), and any servo system adapted to control the attitude ofthe plane in such a manner that these error angles-are reduced to zero,may be employed.

If, for any reason, automatic servo control of the attitude of the craftis not desired, the elevation error angle (Eerror) and the azimuth errorangle (Aerror) could be indicated on suitable indicators, and the pilothimself could manually fly the plane so as to reduce these error anglesto zero, thus correctly positioning the craft.

In Figs. 4A and 4B there is illustrated another embodiment of theinvention comprising a complete inter-aircraft fire control system. Thesystem is adapted to two consecutive modes of operation as designated bythe pilot through suitable switching means. In the first, or search,position of the switches a warning system of suitable type such asdescribed in copending application Serial No. 441,188 for Radio guncontrol system, filed April 30, 1942, in the names of C. G. Holschuh, G.E. White, W. W. Mieher, and J. E. Shepherd provides a visual indicationof the presence, relative direction, and approximate range of otheraircraft in the vicinity. With this information available, the pilot maypick out the most dangerous target, and fly his craft along the line ofsight of that target.

The pilot then switches to track position, which initiates the secondmode of operation. In this position a radio sight which may be of thetype disclosed in copending application Serial No.

444,152 of Holschuh et al., filed May 22, 1942, relating to a Stabilizedtracking and fire control system, is utilized to automatically trackwith the designated target, and provide the computing mechanism with thenecessary information relative to the target in the form of signalvoltages. Stabilizing apparatus for gun sights is well known, astabilizing system being disclosed in the German patent to Anschutz,Serial No. 616,248, August 1, 1935.

The novel electro-mechanical computing mechanism illustrated in Fig. 4Bis adapted to receive this information electrically from the radiotracking system, and to have mechanically set into it data correspondingto indicated air speed (I. A. S.) and altitude (H) of the craft, and tocalculate and transmit, in the form of signal voltage outputs, theelevation and azimuth error angles (Eerror, Aerror). These error angledata are then. used to control suitable servo systems similar ta 8 thoseillustrated in Fig. 1, thus automatically positioning the craft to thecorrect attitude for effectlve gun fire. A visual indication of theelevation and azimuth error angles is also provided on the scanner of asuitable cathode ray indicator tube, so that the pilot may dispense withthe servo system, if desired, and himseli? fly the craft at the correctattitude. Two relays are incorporated in the computing mechanism whichautomatically close two switches, which are connected in series with thegun firing circuit, when both the error angles are substantially zero,thus providing an automatic cut-out feature in the gun firing circuit Ingeneral, the heavy leads of Fig. 4A represent two or more conductorscooperating to carry information, whereas the lighter leads of Fig. 4B

The radio searching, tracking and indicating system is shown in Fig. 4A,and the computing and servo mechanisms are shown in Fig. 4B.

In Fig. 4A there is shown schematically an ultra high frequency radiotransmitting and receiving and scanning system, which includes atransmitter 64 adapted to generate periodic pulses of ultra highfrequency energy and to transmit them, as by wave guides 65 and 65, to ascanner 61. These high frequency pulses are then transmitted throughsuitable wave guides and rotating and stationary joints (not shown) tothe directive antenna 68, which radiates them into space aselectromagnetic energy, the greater portion of the energ beingconcentrated in a direction along the axis of the antenna 68. If, at thetime a pulse is transmitted, there is a target in that direction, thetarget will reflect a portion of the transmitted energy, which energywill then be received by antenna 68, and transmitted to the receiver I09through various wave guides and rotatin and stationary joints (notshown), wave guide 66, T. R. box 60 and wave guide I0. T. R. box 69 isadapted to prevent the transmitted pulses of high energy content fromfeeding directly back into the receiver I09, but allows the receivedpulses of lower energy content to pass. The electron beam of the cathoderay tube I05 is placed under the control of the receiver I09, which,through lead IIO, counteracts the normal off bias of the grid I08whenever a pulse is received, and thus allows a spot to appear on thescreen, The method of operation is well known in the radar art.

The scanner 6'! may be of any suitable type, and preferably is of thekind adapted for search and tracking operations. Generally, suchscanners comprise an antenna which is spun about a spin axis to projecta narrow beam of radiant energy into space for tracking purposes. Forsearching, an additional nodding motion is imparted to the antenna aboutan axis disposed at right angles to the spin axis, the antenna thenprojects, in effect, a solid conical beam of energy, which may cover thegreater part of a hemisphere. Mechanisms for actuating such antennas andselectively controlling the nodding motions thereof are well known andare not within the scope of the present invention so it is not thoughtnecessary to describe here a specific antenna or the controls therefor.An antenna of a suitable type is described and claimed in Patent No.2,410,831, issued November 12, 1946, to L. A. Maybarduk, W. W. Mieher,S. J. Zand and G. E. White. Searching and tracking operations of thescanner Bl shown in Fig. 4A are controlled by a switch is which whenclosed completes an energizing is circuit from battery it through thewinding of a clutch magnet 11. when the switch is open the scannercauses the antenna to nod as it spins, by means, not shown. forsearching. When the switch is closed, the antenna spins, the antennabeing maintained very slightly offset from its spin axis for trackingpurposes.

In track position, therefore, the scanner, in eilect, concentrates onone small portion of the hemisphere, and performs a conical scanningabout that portion. A suitable transmitting and receiving system isdisclosed in the above-mentioned copending application Serial No.441,188.

Two transmitters I3 and 14, connected respectively to the spin and nodaxes, are driven in accordance with the spin and nod motions, re-

spectively, and provide a time reference for these motions.

These transmitters are two phase generators of the self-synchronous typeknown commercially as Selsyn," "Autosyn'. or Telegon" transmitters,shown in detail in Fig. 8. In search position, the nod telegon 14 isshown as energized by a constant source of alternating current I8through leads I9 and 80. The nod telegon is adapted to produce on leadIII a voltage of the same frequency as the source I8, but whoseamplitude continuously varies in accordance .with the nod angle.

This voltage on lead III is transmitted to spin telegon I3 throughswitch SI and lead 92. Spin telegon I3 is adapted to produce in itsoutput lead 94 two voltages of the source frequency, each of which ismodulated with a spin frequency whose amplitude is proportional to thenod angle, the spin modulation frequencies being displaced 90 withrespect to each other. These two voltages are suitably combined intelegon demodulator and filter 93 with a voltage received from thesource I8 through leads I9, 95 and 96, in such away as to produce in theoutput lead 91 two 90 phase displaced voltages of spin frequency and ofan amplitude proportional to the nod angle. One of these voltages isapplied to the horizontal deflecting plates I01 of the cathode rayindicator tube I05 through switch 98, lead 99, switch IM and lead I03.The other voltage is applied to the vertical deflecting plates I06through switch 98, leads 9,! and I00, switch I02 and lead I04.

A suitable circuit for telegon demodulator and filter 93 is shown inFig. 8 Where a nod transmitter I4 is indicated as a two phase generatorhaving its phase windings 300 connected in series to provide a singleoutput. A single phase energizing winding is connected with alternatingcurrent source 18. One terminal of phase windings 300 is grounded whilethe opposite terminal 302 is connected by lead I II to a contact ofswitch 9|.

Spin transmitter I3 is shown in Fig. 8 as having an energizing winding303 having one terminal connected to the lever of switch 9| and theother to ground. Corresponding terminals of the two phase windings 304and 305 are connected to a terminal of the secondary of a transformer306, the other terminal of the secondary being connected to ground. Theprimary of transformer 306 is energized by alternating current from thesource 78. Terminal 308 of phase winding 3001s connected to the plate ofa diode 309 whose cathode is connected to one conductor of circuit 91through a filter circuit which includes choke coil 3 I 0 and condensers3| I.

The output terminal 3I2 of phase winding 305 is connected to the plateof diode 3l3 of a similar demodulator and filter circuit. The cathode ofdiode 3I3 is connected through choke 3 to a second conductor of circuit01. Suitable filter condensers 3|! are connected at Opposite ends ofchoke coil 3. -The voltages flowing from the choke coils 3I0 andJIl areof spin frequency and displaced in phase, their amplitudes beingProportionalto the nod angle as described above.

As is well known, when two voltages of equal frequency and amplitude,but displaced in phase 90 with respect to each other, are applied to thehorizontal andvertical plates, respectively, of a cathode ray tube, theelectron beam is caused to trace out a circle on the screen of the tube,the radius of which circle is proportional to the amplitude of the twovoltages. In the present case, however, the electron beam, if it wereon, would be caused to trace out a spiral, since the amplitude of thetwo voltages is linearly varying in accordance with the nod angle. Thisspiral is in phase with, and corresponds to, the spiral scanningperformed by scanner 61 during search.

However, as previously explained, the electron beam is only allowed tooperate at the time that a pulse is being received. Therefore, a dotwill appear on the screen of the cathode ray indicator tube I05 only atthose points in the latent spiral corresponding to the instants at whicha pulse is received. Fig. 5 illustrates a typical representation of thedots which might appear onthe screen of the cathode ray indicator tubeI05 during search. Thus, each of the dots H6. 6' rep-- resents a target,the orientation of whose line of sight with respect to the spin axis IIcorresponds in elevation and azimuth to the orientation of thatparticular dot with respect to the center of the screen of the cathoderay indicator tube. For instance, the dot IIB represents a. target whoseline of sight coincides with the spin axis II.

A rough range indication is also provided on the screen of the cathoderay indicator tube I05 by the length of the lines III, I II, the lengthhearing an inverse relation to the range. This rough range indication isobtained by superimposing upon the horizontal deflecting plates I01 arapidly oscillating voltage I20, which is initiated at the time of thetransmitted pulse and decreases in amplitude with time. Thus, the closerthe target is, the shorter will be the time elapsed before thetransmitted pulse is received, and the larger will be the oscillatingvoltage and the corresponding range wings III, III. Such an oscillatingvoltage I20 is generated in the range wing circuit II8, which isenergized from transmitter .64, as by lead H9. The required oscillatingvoltage is produced in lead I20 and is transmitted to the horizontaldeflecting plates I01.

To more effectively use this rough range indication, a range scale II3may be etched on the screen of the cathode ray indicator tube, as shownin Fig. 5. v This range scale provides a more accurate indication of therange of a target, when its corresponding spot is at the center of thescreen.

Thus, in search position, a visual indication is provided on the screenof the cathode ray indicator tube I05 of the approximate range of thetarget, and of the target orientation with respect to the spin axis 'IIof the scanner 61.

When switch 9I is in track position, the nod telegon I4 is cut out ofthe circuit, and the spin telegon 13 is energized directly from theconstant source of alternating current 18 through leads I9, 95, H2, and92. The 90 phase displaced voltages of spin frequency produced in lead91 are therefore of constant amplitude in this case. These voltages arefed-into the phase sensitive amplifier I2I, through switch 98 and leadI22.

ted pulse, and The-envelope of these received, pulses will vary at thespin frequency. the amplitude of the variation being proportional to thetracking error. The received pulses are fed through lead I23, switch I24and lead I25 to the detector and filter I28, which is adapted to producein its output lead I21 a spin frequency voltage corresponding to theenvelope of the received pulses. This output voltage I21 is then alsofed to the phase sensitive amplifier I2I.

The phase sensitive amplifier I2I, by comparing the phase of the voltageI21 with that of each of the reference voltages received on lead I22, isadapted to produce in its output leads I28 and I28 unidirectionalvoltages, each corresponding in magnitude and polarity to the magnitudeand sense of the component of the voltage in lead I21 which is in phasewith 'the particular reference voltage with which comparison is made. Asis more fully explained in the aforesaid copending application SerialNo. 441,188, these output voltage signals, appearing in leads I28 andI29, represent the elevation and azimuth components, respectively, ofthe tracking error, that is, the angular deviation of the line of sightof the target with respect to the spin axis 1I. During trackingoperations, the orientation of the spin axis is under the control ofthese voltages I28 and I29 so as to cause the scanner 61 to track with,or follow, the target, as will more fully be explained hereinafter.

Fixed to scanner 81 is a gyro 238 which comprises essentially a rotor(not shown) spinning within a rotor housing 239 about an axis 24I.Housing 239 is pivotally mounted within a ring 2'43 perpendicular toaxis 24I. Ring 243 in turn is pivotally mounted within a further ring248, fixed with respect to the scanner 51, for rotation about an axis244, perpendicular to axis 242. Pivoted within ring 246 about an axis241, perpendicular to axis 244, is a ball ring 248, containing anopening 248 through which passes a shaft 248 coaxial with the gyro axis24I. In this way the ball ring 248 is made to rotate about axis 241together with the gyro axis 24I.

The spin axis H, of the scanner 61, which will hereinafter be referredto as the scanner axis, is orientable in elevation and azimuth withrespect to the axis of the craft about the axes I38 and I3I,respectively. The orientation of the scanner axis II is alwaysmaintained coincident with the orientation of the axis 24I of the gyro238. For this purpose, suitable pick-oils, indicated schematically at256 and 251, are provided which sense any relative displacement alongtwo independent coordinates between the gyro axis 24I and the scannerorientation. The resulting voltages produced in pick-offs 256 and 251are conducted through respective elevation and azimuth amplifiers 258and 258 to the respective control circuits 26I and 262, therebycontrolling the elevation and azimuth servos 238 and 231.

axis 24I.

by rotating the scanner in elevation. Resulting motion of the scanner 81in elevation and azimuth will be in such a direction that the scanneraxis U will align itself with the yro The follow-up system Justdescribed should be made very quick acting, so that the scanner axis 1|will maintain coincidence with the gyro axis 24I even during rapidchanges'in the attitude of the craft.

The orientation of the gyro axis 24I, in turn, is placed underthecontrol of the elevation and azimuth signal voltages in leads I48 and I.respectively. The elevation signal voltage I48 is led to an elevationintegral control circuit I42, which will later be described more fully.The output voltage I48 is then led through a suitable amplifier I43 andthen, by lead I58, to a torque motor I44, which is adapted to apply atorque to ball ring 248 about axis 241, the torque so appliedcorresponding in magnitude and sense to the magnitude and polarity ofthe elevation control voltage I48. The torque thus applied to ball ring248 is transferred to the gyro axis 24I by means of the shaft 248,thereby creating a corresponding torque on the gyro rotor about axis242. This torque, as is well known, will create a precessing motion ofspin axis 24I about the perpendicular axis 244, which motion therebycorresponds to a motion of the gyro axis 24I in elevation.

In a similar manner, th azimuth signal volt- I age appearing in lead MIis led to the azimuth The output of the azimuth servo 231, which 7integral control circuit I45. The output of this circuit is conducted bylead I49, through the azimuth amplifier I46, and then, by lead I5I, tothe azimuth torque motor I41, which is adapted to create a torque onring 243 about axis 244. This torque, therefore, creates a precessingmotion of gyro axis 24I about axi 2'42. This motion corresponds tomotion of gyro axis 24I in slant plane azimuth.

Thus, it is seen that the scanner axis 1| is constantly maintainedcoincident with the orientation of gyro axis 24I, and the orientation ofthe gyro axis 24I, in turn, is placed under the control of the elevationand azimuth signal voltages I48 and I M. Therefore, the scannerorientation is likewise controlled in accordance with the elevation andazimuth signal voltages I48 and MI.

Rotation of the scanner 61 about axis I38 efiects a rotation throughshaft II2 of a potentiometer contact arm I52 which rides on, and makeselectrical contact with, a fixed circular potentiometer resistor I53. Aconstant direct current is caused to fiow in resistor I53, as by batteryI54. One conductor of lead I55 is connected to the mid-point of theresistor I53, which is also the point at which the arm I52 makes contactwhen the scanner is at zero elevation with respect to the plane. Theother conductor of lead I55 is directly connected to the arm I52. Inthis way the voltage across the conductors of lead I55 alwayscorresponds in magnitude and polarity to the magnitude and sense of theangular displacement in elevation of the scanner axis 1I with respect tothe craft axis.

In an identical manner, rotation of scanner 81 about axis I3I efiects arotation of shaft I88 and potentiometer contact arm I51 which rides on,and makes electrical contact with, a second fixed circular potentiometerresistor I58, which is constantly energized from battery I58. In thiscase mid-point EfiI is chosen so that arm lei makes contact with. itwhen the scanner 81 is at zero azimuth with respect to the plane. Thusoutput voltage I62 is always proportional to the angular displacement inazimuth oi! the scanner axis H with respect to the craft axis.

During search position 01' the switches, the elevation voltage I55 makesconnection to the elevation signal voltage lead I40 as by switch I63,lead I64 an'd'switch I65, and thus controls the orientation of the gyroaxis 2 and the scanner axis II in elevation. Similarly; the azimuthvoltage I62 is employed as theazimuth signal voltage I, through switchI66, lead I61 and switch I86. Thus, during search, the elevation andazimuth voltages I55 and I62 are made to control the orientation of thegyro axis 2 and scanner axis 'II so as to maintainthese axes alwayscoincident with the axis of the craft. In other words, during search,the scanner is always pointed in the same direction as the craft.

Also, during search, as has been previously explained, the pilot isprovided with a visual indication on the screen of the cathoderayindicator tube I05 (see Fig. 5) of the presence and relativepositions of all the other craft in the forward'hemisphere. He may thenpick out the most dangerous target, and fly his own craft in .such amanner as to bring the spot represented by that target to the center ofthe screen. In this manner the pilot aligns the craft axis with the lineof sight. That is, he points the craft at the target.

Since, during search, the gyro axis 2 and the scanner axis H aremaintained coincident with the craft axis by the control and follow-upsystem previously described, it is apparent that now all three axes, andalso the line of sight, are identically oriented.

When this condition has been met, as indicated by the central positionof the spot in Fig. 5, the pilot then switches to' track operation ofthe system. At this time the angular relations of the craft and targetare as shown in the first stage of Fig. 3. From this point on, the planewill be automatically controlled by the servo system so as to assume theproper position, as illustrated in the final stage of Fig. 3, to effecta hit. In track position of switches I65 and I68, it can be seen thatthe orientation of the gyro axis MI and the scanner axis II is no longerunder the control of the elevation and azimuth voltages I55 and I62,but, instead, is placed under the control of the voltages I28 and I29which, it has been seen, are proportional to the tracking error, thatis, the angular difierence in elevation and azimuthprespectively,between the orientation of the scanner and the line of sight. In thisway the scanner axis 1| is made to track with, or follow, the target.Thus, in track position the gyro axis 2 and the scanner axis 1I and theline of sight are all maintained coincident by the control and follow-upsystem, their positions being in this case independent of theorientation of the craft itself.

As is more fully-explained in previously mentioned copending applicationSerial No. 444,152, when the scanner is caused to track with the targetin elevation and azimuth under the control of the precessing torquesapplied by torque motors I44 and I41, respectively, the signal voltagesI50 and I5I applied to these torque motors are proportional in polarityand magnitude to the sense and magnitude of the angular rates (Er, Ar)of the target in elevation and azimuth, respectively, with respect tothe standard or reference of position. These voltages I50 and I5I maythen be conducted through switches I1! and I10, re-

spectively, to the elevation and azimuth angular rate '(Er, Ar) voltagesignal leads I12 and I18, respectively, thus'supplying this rate data tothe computing mechanism shown in Fig. 4B.

Actually, the azimuth angular rate voltage signal I13 thus produced isproportional to the slant plane azimuth rate, whereas the true azimuthrate should be set into the computing mechanism. Although a correctioncould be incorporated in the computing mechanism to convert the slantplane azimuth rate to the true azimuth rate, the

*actual difference between the two is extremely small and can beneglected. This is particularly true in the present system, since, whenthe craft is correctly positioned, the elevation of the line of sight(E0) with respect to the craft will be equal and opposite to theelevation lead angle AE (as illustrated in Fig. 3 for azimuth), whichwill ordinarily be very small.

It is desired to have the scanner 61 track accu- V rately with thetarget, a condition which necessarily results in the voltages I28 andI29 being zero, and at the same time to have voltage signals existing inleads I50 and I 5i, in order to obtain rate data for the computingmechanism. For this purpose, the elevation and azimuth integral controlcircuits I42 and I45 are employed.

The elevation and azimuth integral control circuits I42, I45 areidentical and may be of the type illustrated in Fig. 7 for elevationintegral control. As there shown, the circuit consists of four resistorsI14, I15, I16 and I11, respectively, placed in series with the controlvoltage I40. Across the last two resistors I16 and Ill, there are placedin parallel a condenser I18 and a fifth resistor I19. Output conductor I8| is connected to tap I84 between resistors I14 and I16, and 7amplifier, which, in this instance, would include two electron tubesoperated in push-pull.

When a signal voltage first appears on control voltage lead I40, thecondenser I18 is uncharged, and the output signal voltage acrossconductors I 8i and I83 will be composed merely of the sumof the voltagedrops across resistors I 16, I19 and I11, and will therefore beproportional to the control voltage I40. However, if this condition ismaintained for a short time, the condenser I18 will charge. Now, if thecontrol voltage I40 is reduced to zero, the voltage across the condenserI18 will be maintained until it discharges through resistor I19, andthis voltage will continue to appear as an output voltage across theconductors I8I and I83. I 1

Thus, by choosing the proper circuit constants adapted to provide asuitable time constant for the circuit, it is possible to have an outputcontrol voltage appear in lead I48, which may be used to control theorientation of scanner 61, and to provide the necessary rate data forthe computing mechanism, and still have practically no signal voltageappearing in lead I40, that is, no elevation tracking error. The azimuthintegral control circuit I45 operates in the same manner so as tomaintain an output voltage signal in lead I49 after the input controlvoltage I4l has been reduced to zero by the elimination of the azimuthtracking error.

The voltage signals I55 and I62 are indicative 15 of the orientation ofthe scanner 61 with respect to the craft. Since, during track positionof the switches. the scanner axis H is maintained coincident with theline of sight, the voltage signals I55 and I62correspond in magnitud andpolarity to the magnitude and sense of the elevation and azimuth angles,respectively, which the line of sight makes with respect to the craft,that is, to E and A0. The voltages I55 and I62, t erefore. are connectedthrough switches I and I66, respectively, to leads I86 and I81, thussupplying present elevation and present azimuth angle (E0, Ao) voltagesignals, respectively, to the computing mechanism.

Data corresponding to present range (Do) is automatically introducedinto the computing mechanism as a voltage signal appearing in lead I88..In order to obtain this range signal voltage I88, an automatic rangecircuit is employed. This automatic range circuit is preferably of thetype disclosed in copending application Serial No, 434,483, for Pulsereceiving systems, filed March 12, 1942, in the name of H. M. Stearns.Such a circuit, when supplied with information relative to the time oftransmission of the pulse, as by lead I88, switch I8I and lead I92, andalso with similar information relative to the time of receiving the 16lead I 84. The azimuth error angle (Aerrer) voltage signal I88, I98 issimilarly applied tothe horizontal deflecting plates I81 of the cathoderay indicator tube I85, asrby conductors 288, lead 2I8, switch IM andlead I83, along with the oscillating voltage I28 from the range wingscircuit I I6.

Thus, as is illustrated-in Fig. 6, the screen of the cathode rayindicator tube I88 will provide,

.during tracking operation, a continuous visual corresponding reflectedpulse, as by lead I83,

switch I94, and lead I95, is adapted to produce, as on output lead I88,a unidirectional voltage, the magnitude of which corresponds to the target range (Do).

Thus, the computing mechanism, shown in Fig. 43, having received, asvoltage signal inputs, all the necessary data for the complete solutionof the inter-aircraft fire control problem, computes the elevation errorangle (Eerror) and the azimuth error angle (Aerror), as will behereinafter described in more detail, and produces this information asunidirectional voltage signals across the conductors I96, I91 and I88,I98, respectively.

The elevation error angle (Eerror) voltage signal across leads I86, I91is amplified in the elevation amplifier 288, and then fed to theelevator servo 28I, which may be identical to the aileron servoillustrated in Fig. 2, thus controlling the elevators, and consequentlythe orientation of the craft in elevation, so as to decrease theelevation error angle (Eerror) to zero.

Similarly, the azimuth error angle (Aerror) signal voltage across theconductors I88, I89 is amplified in azimuth amplifier 282, and then fedto the rudder servo 283, which may also be identical to the aileronservo illustrated in Fig. 2, and which correctly orients the craft inazimuth by operating on the rudder so as to reduce the azimuth errorangle (Aerror) to zero.

The elevator servo 28I and rudder servo 283, operating under the controlof the elevation and azimuth error angle (Eerror, Aerrer) voltagesignals I86, I81 and I88, I99, respectively, will thus correctlyposition the craft (and the guns) to the correct orientation to effect ahit.

An aileron control system, indicated schematically as comprising apendulum control 284, an aileron amplifier 285, and an aileron servo286, is incorporated in order to provide the correct angle of bank forthe craft during operation of the rudder servo. This aileron controlsystem may be exactly the same as is shown in Figs. 1

and 2.

The elevation error angle (Eerror) voltage signal I96, I81 is alsoapplied to the vertical deflecting plates I86 of cathode ray indicatortube i585, as by conductors 281, lead 288, switch E82 and indication forthe pilot of the elevation error angle (Eerrer), the azimuth error angle(Aerror), and the approximate range (D0) of the target. The dots 2I I,2| I and 2I I" ilustrate the azimuth error angles which would besuccessively indicated at the three stages in the solution shown in Fig.3. In the final stage the dot is at the center, indicating that both theelevation error angle (Eerror) and the azimuth error angle (Aerror) arezero, and that a projectile fired at that time will effect a hit,provided only that the indicated range is within that of the guns beingused. If this latter condition is met, the pilot may maintain his firingkey closed, and the guns will be automatically caused to fire when botherror angles are zero, by virtue of the automatic gun firing circuit,which will be presently described.

Obviously, if desired, the pilot may remove the craft from the controlof the automatic pilot systorn by a suitable clutch or switch (notshown), and himself fiy the craft in such a way as to bring the dot tothe center.

In the previous discussion of the operation of the system of the presentinvention during search, it will be remembered that the scanner axis wasmaintained coincident with the craft axis through the control andfollow-up system, and the craft was then oriented by the pilot so as toalign both of these axes with the line of sight. It should be stressedthat the coincidence of these three axes is not a necessary'conditionfor initiating the tracking operation, it being sufficient that thescanner axis alone coincides with the line of sight.

Therefore, the system could be modified, if desired, by removing thescanner from the control of the control voltages I55 and I62, whichnormally operate, in search position, through the follow-up system, tomaintain the scanner axis aligned with the craft axis, and instead toplace the scanner axis directly under the manual control of the pilot,who could then align the scanner axis. with the line of sight bypositioning the scanner itself instead of the craft and the scanner.

However, the system as first described, with the scanner axis maintainedcoincident with the plane axis, and the plane being then positioned bythe pilot into alignment with the line of sight is the preferredembodiment of the invention, since by flying the plane in the directionof the line of sight, the pilot himself performs the first approximationto the complete solution. This is clearly indicated from the angularrelation-s illustrated in the first stage of Fig. 3 in which theelevation error angle (Eerror) and azimuth error angle (Aerror) arerespectively equal to the elevation lead angle (AE) and azimuth leadangle (AA), both of which are normally small. The preferred system,therefore, performs the first approximation to the solution for thecomputing mechanism. Also, by preventing large error angle voltagesignals from initially being fed to the automatic pilot system, shock onthis system is reduced, and the possibility of the craft gettingcompletely out of control by too rapid changes in attitude is prevented.

to=f(Do) X-f(H) XML .4. s.)

where Do represents the present range of the target, H the altitude ofthe craft, and I. A. S. the indicated air speed.

The pilot turns the altitude dial 2I2 until the fixed index 2I3 isopposite the correct altitude. The dial 2I2 is so graduated that thenecessary rotation required to accomplish this is proportional to thelogarithm of a predetermined function of the altitude (H). Thus, logf(H) is set into the differential 2I6 through the shaft 2I4.

In a similar way log ,f(I. A. S.) is set into a second diiierential 2I9through shaft 2I8 by rotation of the indicated air speed dial 2I6 untilthe fixed index 2I1 ,reads the correct indicated air speed.

The range voltage signal I88 is conducted by conductors 220 to the rangefollow-up 22I, which is of any suitable type adapted to produce anangular displacement of its output shaft 222 proportional to the inputsignal voltage I88. Shaft 222 rotates logarithmic cam 223, which isdesigned so as to produce a linear displacement of its follower 224which is proportional to the logarithm of a predetermined function ofits own angular displacement. The linear displacement of follower 224,which is therefore proportional to log f(Do), is converted to an angulardisplacement of shaft 226, as by rack 229 and'pinion 225, and. is thentransmitted to the differential 2I5 through gearing 221 and shaft 228.

The differential 2I5 mechanically performs an addition of the rotationof input shaft 228 (log f(Do)) and the rotation of the second inputshaft 2I4 (log j(H)) and produces on its output shaft 239 a rotationproportional to their sum (log f Do+log ,f(H) The second differential 2|9, in like maner, adds together the angular displacements of its twoinput shafts 239 and 2| 8 and produces on its output shaft 23l anangular displacement proportional to their sum Shaft 23I rotates asecond logarithmic cam 232, which is adapted to produce a, lineardisplacement of itsfollower 233 proportional to the antilogarithm of itsown angular displacement. Thus, on

the basis of the formula for (to) previously mentioned, it is apparentthat the linear displacement of follower 233 isproportional to the timeof flight (to). The linear displacement of follower 233 ls converted toa proportional angular displacement of shaft 269 through the rack 234and pinion 235. The shaft 236 then causes the contact arms 210 and 21Ito be rotated on their respective potentiometer resistors 212 and 213 anangle proportional to time of flight (to).

The azimuth rate (Ar) voltage signal I13 is applied across the terminalsof the azimuth potentiometer resistor 213, as by conductors 214 and 215.The voltage drop across the terminal tap 216 and the conductor I98,which is electrically connected to the contact arm 21 I, will thereforebe proportional to both the azimuth rate (Ar) voltage signal I13 and theangular displacement of the contact arm 2". Thus, the voltage I98, 218is proportional to the product of azimuth rate ,(Ar) and time of flight(to) and therefore is proportional to the azimuth lead angle (AA) Thisazimuth lead angle (AA) voltage I98, 218 is placed in series with thepresent azimuth (A0) voltage I81, the two voltages being therebyalgebraically added together. to produce the azimuth error angle(Aerror) voltage I98, I99, according to the formula,

- The elevation error angle (Esrror) voltage I88, I91 is obtained in asimilar manner. Thus, the elevation rate (Er) voltage I12 is appliedacross the terminals of the elevation potentiometer resistor 212, as byconductors 218 and 218. However, in this case a small constant directvoltage, such as the battery 280, is first inserted in series with oneof the elevation rate voltage conductors 218. The battery voltage 288 ischosen so as to be proportional to the ratio of the superelevationcorrection (s) to the time of flight (to), which ratio is substantiallyconstant. The actual voltage 28I, 282 across the elevation potentiometerresistor 212 will, therefore, be proportional to the sum of theelevation rate (Er) voltage I12 and the constant battery voltage 280 Thevoltage I96, 28I across the contact arm 219 and one terminal of thepotentiometer resistor 212, being proportional both to the voltage 28I,

282 and to the angular displacement of the contact arm 218, proportionalto the product of and to, and is therefore proportional to the elevationlead angle (AE) according to the formula,

In series with the leads 23, 24 to the gun firing circuit, there areshown two switches 285 and 286 which are under the control of theelevation relay 283 and the azimuth relay 284, respectively.

The elevation relay 283 is energized by the elevation error angle(Eerror) voltage I96, I91, so that switch 285 is allowed to close onlywhen the elevation error angle is substantially zero. The azimuth relay284 is similarly energized from the azimuth error angle (Aer-rot)voltage I98, I99 so that switch 288 is allowed to close only when theazimuth error angle is substantially zero. In this way an automatic gunfiring circuit 23, 24

is provided, which the pilot can only close when both elevation errorangle (Eel-m) and azimuth error angle (Aerror) are substantially zero,that is, when the craft (and the guns) have been correctly oriented toeffect a hit on thetarget;

Figures 4A and 4B show one form of computer controlled by a stabilizedsight, the output from the stabilized'sight being the target rates Erand A: in elevation and azimuth, respectively, and

E and A0, the angular position of the target in elevation and azimuth,respectively. These outputs are available from any stabilized line ofsight defining device and could be used to actuate any other suitablecomputer such as that shown in the diagram of Fig. 1. If the stabilizedsight is not of the radar type, where an accurate measure of range isusually available, the shaft 8 of Fig. 1 could be operated according torange obtained from any range finder. The output shafts l I and ii areshown as controlling directly the servos l and I5 for an automaticpilot. The altitude and indicated air speed handwheels 2 and 4 are wellknown in modern airborne sights to provide correctionsin the ballisticsfor air speed, ,corrected for air density. That is, these handwheelssupply a correction for ballistic wind on the pro- Jectiles due to themotion of the supporting aircraft. The effect of the wind variesaccording to air density, the air becoming less dense as the altitudeincreases. These corrections are introduced in various ways in thedifl'erent types of computers and are well known to those skilled in theart.

As many changes could be made in the above construction and manyapparently widely diiferent embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In an automatic fire control system for a gun supported in a fixedposition on an aircraft, target tracking means, a lead angle computingmechanism, controlled thereby adapted to solve for the corrections tothe orientation of the supporting aircraft necessary for effective gunfire, and automatic pilot means controlled according to said computedcorrections for positioning the aircraft to the proper orientation foreffective un fire.

2. In an automatic fire control system for a gun supported in a fixedposition on an aircraft. target tracking means, a lead angle computingmechanism controlled thereby adapted to solve for the corrections to theorientation of the supporting aircraft necessary for effective gun fire,in terms of elevation and azimuth, automatic pilot means for positioningthe craft, and means controlled by the output of the computing mechanismfor actuating said automatic pilot means in accordance with saidcomputed corrections.

3. The apparatus described in claim 1, further including, a gun firingcircuit, and automatic cut-out means under the control of the output ofthe computing mechanism according to said computed corrections formaintaining said firing circuit open except when said computedcorrections are substantially zero. g

4. The apparatus described in claim 1, further including, an electricalgun firing circuit, auto- 20 orientation of the supporting aircraftnecessary for-directing effective gun fire at the target, and automaticsteering means operated by the computing means for contro'ling theorientation of the supporting aircraft to position the gun in accordancewith said computed corrections.

6. A fire control system for a gun supported in a fixed position on anaircraft comprising sighting means for tracking a target, lead anglecomputing means operated thereby for computing from target trackingoperation the corrections to the orientation of the craft necessary foreffective gun fire, and servo motor means actuated by the output of thecomputing means for controlling the orientation of the craft to positionthe gun in accordance with said computed corrections.

7. In a fire control system for a gun supported in a fixed position onan aircraft, target tracking means, a lead angle computing mechanismcontrolled thereby adapted to solve for the corrections to theorientation of the craft necessary to position the gun for effective gunfire, and means comprising a cathode ray tube controlled by thecomputing mechanism for providing an indication of said lead anglecorrections for the pilot, whereby the pilot may manually position thecraft to the correct orientation for effective gun fire.

8. Apparatus, as described in claim '7, wherein said indicating meansalso provides an indication of target range, whereby the pilot may knowwhen the target is within gun range.

9. Apparatus, as described in claim 7, wherein said indicating meansalso provides an indication of target range, and further including, anelectrical gun firing circuit, switching means in said gun firingcircuit, and actuating means under the control of said computingmechanism for closing said switching means when said computedcorrections are substantially zero.

10. An automatic fixed gun inter-aircraft fire control systemcomprising, a sight adapted to be rotated in elevation and azimuth, afree stabilizing gyro cooperating with said sight, means for controllingthe orientation of said sight in accordance with the orientation of saidgyro, means for producing control torques in accordance with thenon-coincidence between the axis of said sight and the true line ofsight to a target, means for controlling the orientation of said gyrofrom said control torques, computing means for computing the correctionsto the orientation of the craft necessary for effective gun fire interms of elevation and azimuth, means for providing target range inputdata for said computing means, means for transmitting target elevationand azimuth input data corresponding to. the orientation of said sightto said computing mechanism, means for transmitting target elevation andazimuth stabilized rate input data corresponding to said control torquesto said computing means, and automatic pilot means controlled by theoutput of the computing means for positioning the craft in accordancewith said computed corrections.

11. An automatic fixed gun inter-aircraft fire control system, asdefined in claim 10, further including, an electrical gunfiring circuit,automatic switching means in said gun firing circuit, means for closingsaid switching means when said computed corrections are substantiallyzero, other switching means in said firing circuit under the manualcontrol of the pilot, and means for providing an indication of targetrange for the pilot.

12. An automatic fixed gun inter-aircraft fire control system, asdefined in claimilo, wherein said means for producing control torquesincludes integrating means adapted to allow the production ofsubstantial control torques from substantially zero degrees ofnon-coincidence between the axis of said sight and the true line ofsight to said target.

13. A fixed gun inter-aircraft fire control system, as defined in claim10, further including means for providing an indication of target rangeand also of said computed corrections for the pilot, and switching meansfor releasing the craft from the control of said automatic pilot means.whereby the pilot may manually fiy the craft to the orientationnecessaryfor effective gun fire.-

14. A fixed gun inter-aircraft fire control system comprising meansincluding a scanner, rotatable in elevation and azimuth, for directingelectromagnetic energy at a target for searching and trackingoperations, means for receiving the corresponding reflected energy, astabilizing free gyro associated with said scanner, means forcontrolling the orientation of said scanner from the orientation of saidgyro, torque producing means for controlling the orientation of saidgyro, switching means for selectively initiating either searching ortracking operations, means for placing said torque producing means underthe control of the craft orientation during search, and under thecontrol of the target position, as determined by .the variations in saidrefiected energy during track, means for indicating the orientation ofthe line of sight to the target with respect to the craft during search,and computing means for computing, during track, the corrections to theorientation of the craft necessary for effective sun fire.

15. An automatic fixed gun inter-aircraft fire control system, asdefined in claim 14, including further, automatic pilot means under thecontrol of said computing means according to the computed correctionsfor positioning the craft at the orientation necessary for effective gunfire,

16. A fixed gun inter-aircraft fire control system, as defined in claim14, including further, means for indicating the target range, andautomatic pilot means under the control of said computing means forpositioning the craft to the orientation necessary for effective gunfire.

17. A fixed gun inter-aircraft fire control sysvtem, as defined in claim14, including further,

visual means for indicating to the pilot during track the target rangeand also said computed corrections, whereby the pilot may manuallyorient the craft for effective gun fire.

18. A fire control system for a gun mounted in a fixed position on anairplane comprising a. radar system for tracking a. target, meanscontrolled by the radar system for computing the lead angles forpositioning the gun so that projectiles therefrom will strike thetarget, and steering means for the aircraft controlled jointly by theradar system and computing means for a positioning the gun according tothe computed lead angles.

19. A fire control system for a gun mounted in a fixed position on anairplane comprising a radar system for tracking a target, means includedin the radar system for computing the lead angles necessary forpositioning the gun so that projectiles therefrom will strike thetarget, indicating means in the-radar system controlled by the computingmeans for constantly indicating the magnitude of the error of theposition ing a target for computing the lead angles necessary forpositioning the gun so that projectiles therefrom will strike thetarget, indicating means comprising a cathode ray tube included in theradar system and controlled by the computing means for constantlyindicating the magnitude of the error of the position of the gun withrespect to the computed lead angles in order that the progress of theplane may be observed as it is being guided to a position where no errorexists in the position of the gun.

21. A fire control system for pursuit planes having an automatic pilotand a gun mounted in a fixed position on said plane, comprising a radarsystem for tracking the target, means controlled thereby for computingproper lead angles for the gun, and means controlled by said lead anglecomputing means and operating through said automatic pilot for steeringthe craft along such course as to cause the proper lead angles to bemaintained by the fixed gun.

22. A fire control system for use against invisible targets for anaircraft having fixed guns which comprises a radar line of sight definindevice movable with respect to the aircraft for target trackingpurposes, a computer controlled by the line of sight defining device forcomputing constantly the lead angle at which the guns on the aircraftmust be positioned for effective gun fire against the target, and meanscontrolled by the output of the computer for indicating the visibletargets, for aircraft having fixed guns,

which comprises a radar line of sight defining device movable withrespect to the aircraft for target tracking purposes, a computercontrolled by the line of sight defining device for computing constantlythe position required for the aircraft in order that the guns fixedthereto may lead the target according to the lead angle required foreffective gunfire, and means comprising a cathode ray indicator tubehaving circuits controlled by the line of sight defining device and bythe output of the computer for indicating the position of the targetwith respect to the aircraft, the position indication varying accordingto the difference between the instantaneous position of the aircraft andthat computed by the computer.

24. A fire control system adapted for use at night by an aircraft havingfixed guns which comprises a radar target tracking device including acathode ray indicator, a computer controlled by the radar device forcomputing the lead angle by which the guns must be offset from the radarline of sight for effective gunfire against the target being tracked,and circuit means for the cathode ray indicator controlled by the radardevice and by the output of the computer effective to cause theindicator to indicate the present position of the aircraft with respectto that in which the guns are positioned according to the computed leadangle.

25. A fire control system adapted for use at night by an aircraft havingfixed guns which comprises a radar target tracking device including acathode ray indicator, a computer actuated by the tracking deviceaccording to range, the angular position of the target and rate ofchange thereof for computing lead angles for the guns, circuit meanscontrolled by the output of the computer and by the tracking device forso controlling the cathode ray indicator that a constant indication isprovided thereby of the present position of the target offset from areference in accordance with the instantaneous magnitude of the computedlead angle.

26. A fire control system adapted for use at night by an aircraft havinguns fixed parallel to the longitudinal axis thereof which comprises aradar target tracking device including a cathode ray indicator, 8.computer actuated by the tracking device according to 'range, theangular position of the target and rate of change thereof for computinglead angles for the guns, circuit means controlled by the output of thecomputer and by the tracking device for so controlling the cathode rayindicator as to obtain a constant indication of the present position ofthe target offset from a reference in accordance with the instantaneousmagnitude of the computed lead angle whereby the aircraft may be flownto position the guns at the required lead angles whereupon theindication of the target will coincide with the reference.

27. A fire control system particularly'adapted for use against invisibletargets and in connection with aircraft having fixed longitudinallydisposed guns which comprises a radar target tracking device including acathode ray indicator present position of the target ofiset from areference, the offset being in accordance with the computed lead angle.

28. A fire control system particularly adapted for use against invisibletargets and in connection with aircraft having fixed longitudinallydisposed guns which comprises a radar target tracking device including acathode ray indicator having my deflecting means, a computer actuated bythe tracking device according to range, the angular position of thetarget with reference to the aircraft and the rate of change thereof forcomputing lead angles for the guns, circuit means connected with the raydeflecting means controlled by the output of the computer and by thetracking device for actuating the cathode ray tube to form an indicationof the present position of the target offset from a reference accordingto the computed lead angle, and automatic pilot means controlled by thecircuit means for guiding the aircraft to a position wherein the gunsthereon are positioned according to the computed lead angle.

EDMUND B. HAMMOND, J R. GIFFORD E. WHITE.

REFERENCES CITED The following references are of record in the file ofthis patent:

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